Concentration photovoltaic CPV technology uses optics such as lenses or curved mirrors to concentrate a large amount of sunlight onto a small area of solar photovoltaic PV cells to generate electricity. They therefore function under high concentration of light (normally more than 100 suns).
Compared to non-concentrated photovoltaic systems, CPV systems can save money on the cost of the solar cells, since a smaller area of photovoltaic material is required. As a smaller PV area is required, CPVs can use higher-efficiency solar cells. To get the sunlight focused on the small PV area, CPV systems require costly optics (lenses or mirrors), solar trackers, and cooling systems. Because of these additional costs, CPV is far less common today than non-concentrated photovoltaic.
FIG. 7 depicts an exemplary CPV system 700 of the prior art composed of at least one CPV device 710 for receiving and converting the received light energy into electrical energy. In essence the CPV device is a photoelectrical transducer. Additionally, CPV systems comprise external solar position sensors 720 in order to aid them in aligning correctly with the constantly changing sun position. The sensor transmits the solar position information via link 730.
A CPV device usually comprises at least one primary optical element POE that concentrates incoming light onto at least one CPV receiver. Current systems typically comprise a plurality of POEs and CPV receivers. Additionally, as mentioned before, CPV devices comprise solar trackers in order to keep the CPV device aligned with respect to the sun, as an accurate aligning with respect to the sun is critical for the device performance.
In the development of CPV systems there have been many different approaches for the fine tuning of solar tracking control systems. Some concentration tracking systems only work in open loop, but the vast majority of them follows a hybrid or purely closed loop tracking algorithm. While open loop systems rely on astronomical calculations to keep the CPV device correctly aligned, close loop systems use feedback signals or images coming from the solar position sensor, or camera, and therefore require following the sun along two axes with high accuracy.
The hybrid type comprises a combination of open and closed loop tracking, in other words, the hybrid algorithms rely partially in both astronomical calculations and the feedback signals provided by external sensors. These external sensors need a precise alignment with the CPV device's optical axis in order to work properly. As the objective of the tracker system is to align the CPV devices with respect to the sun, any slight mechanical misalignment between the sensor and the modules downgrades the overall performance of the CPV system. The requirement for field alignment increases deployment costs and increases the probability of having recurrent problems. If the sensor has to be calibrated to each tracking system then this procedure is critical and it can be prone to develop mechanical misalignment, requiring periodical maintenance.
Another common problem for solar position sensors of the prior art is that they can be fooled by clouds or ground reflections, therefore misleading the tracking control algorithm actually making it follow other objects, and therefore losing energy productivity.
Additionally, external solar sensors must rely on small aperture optics in order to minimize its impact on the overall CPV module's solar aperture, so that they are prone to be affected by dirt stains or soiling.
Yet another problem of known solar position sensor designs for CPV systems is that they have a very narrow acceptance, in such a way that if the sun does not lie within its angle of vision they are not able to correct the misalignment. This means that under some failure modes these sensors are not able to help the system recover its right position.
Also, these external sensors constitute completely redundant optical systems working in parallel with the CPV module optics. Having a different optical system makes it difficult to match the CPV module's characteristics and implies a redundancy of components which is not optimal and increases system costs. A CPV system is necessary that does not need redundant optical systems and does not have an impact on the CPV's solar aperture
The present invention has the goal of solving the aforementioned problems, by means of increasing tracking system reliability and reducing manufacturing, commissioning, operation and maintenance costs.